A new genetic variation of the malate dehydrogenase-like enzyme (MDL-1) in inbred rats and its possible linkage

The gene map of the Norway rat (Rattus norvegicus) and comparative mapping with mouse and man

The current status of the rat gene map is presented. Mapping information is now available for a total of 214 loci and the number of mapped genes is increasing steadily. The corresponding number of loci quoted at HGM10 was 128. Genes have been assigned to 20 of the 22 chromosomes in the rat. Some aspects of comparative mapping with mouse and man are also discussed. It was found that there is a good correlation between the morphological homologies detectable in rat and mouse chromosomes, on the one hand, and homology at the gene level on the other. For 10 rat synteny groups all the genes so far mapped are syntenic also in the mouse. For the remaining rat synteny groups it appears that the majority of the genes will be syntenic on specific (homologous) mouse chromosomes, with only a few genes dispersed to other members of the mouse karyotype. Furthermore, the data indicate that mouse chromosome 1 genetically corresponds to two rat chromosomes, viz., 9 and 13, equalizing the difference in chromosome number between the two species. Further mappings will show whether the genetic homology will prove to be as extensive as these preliminary results indicate. As might be expected from evolutionary considerations, rat synteny groups are much more dispersed in the human genome. It is clear, however, that many groups of genes have remained syntenic during the period since man and rat shared a common ancestor. One further point was noted. In two cases groups of genes were syntenic in the mouse but dispersed to two chromosomes in rat and man, whereas in a third case a group of genes was syntenic in the rat but dispersed to two chromosomes in mouse and man. This finding argues in favor of the notion that the original gene groups were on separate ancestral chromosomes, which have fused in one rodent species but remained separate in the other and in man.

Genetic variability in SHR (SHRSR), SHRSP and WKY strains

Genetic background for SHR (SHRSR) and SHRSP and WKY lines were screened by using biochemical genetic markers and class I major histocompatibility complex (RT1) typing. There were many kinds of SHR (SHRSR), SHRSP and WKY inbred lines. The genetic variabilities within SHR (SHRSR) or SHRSP strains were small, but those within WKY strains were not so small. When SHR lines were compared with WKY lines, the allele distribution in SHR lines was different from that in WKY lines at 3-13 loci. Three genetic markers, the Es-3b, Es-4a and PT1k, were identified as specific markers of SHR (SHRSR) and SHRSP. WKY/Izm, WKY/Hos, and WKY/Jim also carried the PT1k as well as SHR lines, but WKY/N and WKY/NCrj had the RT1l haplotype.

Linkage of neutrophil response to a mutagen gene (Nrm-1) to the agouti locus in the rat

The ACI or BDIV rats responded with decreased or increased neutrophil levels in blood after the N-methyl-N-nitrosourea (MNU) administration. The F1 hybrids had decreased neutrophil counts, and the BDIV x (BDIV x ACI)F1 backcross offspring showed two phenotypes. The sex of the rats and the neutrophil response to MNU assorted independently. The results indicated that the neutrophil response to MNU was regulated by autosomal gene Nrm-1 with two alleles. The Nrm-1d regulates the decrease and the Nrm-1i regulates the increase of neutrophils in blood after the MNU administration. The results were confirmed by the SKUMIX computer program. We found that the Nrm-1 gene was linked to the agouti locus (chi-square = 10.3, P less than 0.001). The map distance between two genes was 33 +/- 5 cM. The Nrm-1 gene thus resides on the linkage group IV of the rat.

Linkage of diabetes insipidus and agouti genes in the rat

Linkage of the hooded (h), agouti (A), and diabetes insipidus (di) genes was found in (ACI X DI)F1 X DI backcross rats. The genetic map distance A-di for females and for males was 19 +/- 5 and 28 +/- 5 cM, respectively. However, this difference was not significant. The combined data showed the map distance to be 25 +/- 4 cM. The three-point cross showed the following corrected distances and order of genes: h-42 +/- 4-A-25 +/- 4-di. However, the linkage of h and A, although significant (chi 2 = 9.03, P less than 0.001), is only tentative and must be confirmed by additional studies.

Enzyme markers in inbred rat strains: genetics of new markers and strain profiles

Twenty-six inbred strains of the laboratory rat (Rattus norvegicus) were examined for electrophoretic variation at an estimated 97 genetic loci. In addition to previously documented markers, variation was observed for the enzymes aconitase, aldehyde dehydrogenase, and alkaline phosphatase. The genetic basis of these markers (Acon-1, Ahd-2, and Akp-1) was confirmed. Linkage analysis between 35 pairwise comparisons revealed that the markers Fh-1 and Pep-3 are linked. The strain profiles of the 25 inbred strains at 11 electrophoretic markers are given.